A brushless motor includes a stator having three-phase coils U, V, W and a rotor having a field permanent magnet, and a sensor magnet that is rotated together with the rotor is attached to a rotation shaft of the rotor. The sensor magnet is magnetized by S and N poles alternately in a rotation direction. Three Hall sensors that detect a rotation position are attached to the vicinity of the sensor magnet at an interval of 120° in the rotation direction such that it is possible to detect the switching of magnetic poles of the sensor magnet.
In a motor control apparatus that controls and drives the brushless motor, switching positions of three Hall sensors are used as criteria, and by outputting a power distribution pattern that corresponds to each of Hall stages to an inverter circuit that drives the brushless motor, the brushless motor is rotated.
FIG. 4 is a view showing a time chart of position detection signals Hu, Hv, Hw of the three Hall sensors when performing a drive control of the brushless motor. In FIG. 4, a horizontal axis represents an electric angle and a vertical axis represents a voltage level of the position detection signal. As shown in FIG. 4A, the motor control apparatus has a configuration that outputs a drive signal which switches a switching element of the inverter circuit on the basis of a Hall edge that forms each of six Hall stages 1 to 6 which are represented by the combination of electric potentials of the position detection signals Hu, Hv, Hw that are outputs of the three sensors. A time period (a time period of a Hall stage) between two Hall edges that form each of the six Hall stages 1 to 6 corresponds to an electric angle 60° of a time period of a Hall stage.
That is, the time period of a Hall stage 1 corresponds to an electric angle 60° of a time period between a Hall edge which is a rising time point of the position detection signal Hu and a Hall edge which is a falling time point of the position detection signal Hw. The time period of a Hall stage 2 corresponds to an electric angle 60° of a time period between the Hall edge which is a falling time point of the position detection signal Hw and a Hall edge which is a rising time point of the position detection signal Hv. The time period of a Hall stage 3 corresponds to an electric angle 60° of a time period between the Hall edge which is a rising time point of the position detection signal Hv and a Hall edge which is a falling time point of the position detection signal Hu. The time period of a Hall stage 4 corresponds to an electric angle 60° of a time period between the Hall edge which is a falling time point of the position detection signal Hu and a Hall edge which is a rising time point of the position detection signal Hw. The time period of a Hall stage 5 corresponds to an electric angle 60° of a time period between the Hall edge which is a rising time point of the position detection signal Hw and a Hall edge which is a falling time point of the position detection signal Hv. The time period of a Hall stage 6 corresponds to an electric angle 60° of a time period between the Hall edge which is a falling time point of the position detection signal Hv and a Hall edge which is a rising time point of the position detection signal Hu.
In the time period of the Hall stage 1, a Hall pattern 5 that represents the combination of electric potentials of the position detection signals Hu, Hv, Hw is (H (high), L (Low), H). In the time period of the Hall stage 2, a Hall pattern 1 that represents the combination of electric potentials of the position detection signals Hu, Hv, Hw is (H, L, L). In the time period of the Hall stage 3, a Hall pattern 3 that represents the combination of electric potentials of the position detection signals Hu, Hv, Hw is (H, H, L). In the time period of the Hall stage 4, a Hall pattern 2 that represents the combination of electric potentials of the position detection signals Hu, Hv, Hw is (L, H, L). In the time period of the Hall stage 5, a Hall pattern 6 that represents the combination of electric potentials of the position detection signals Hu, Hv, Hw is (L, H, H). In the time period of the Hall stage 6, a Hall pattern 4 that represents the combination of electric potentials of the position detection signals Hu, Hv, Hw is (L, L, H). In this way, the motor control apparatus has a configuration that outputs a drive signal which switches the switching element of the inverter circuit on the basis of the Hall edge that forms each of the six Hall stages 1 to 6 which are represented by the combination of electric potentials of the position detection signals Hu, Hv, Hw that are outputs of the three sensors.
FIG. 4A described above shows an ideal state in which the time period between two Hall edges that form each of the six Hall stages 1 to 6, that is, the time period of the Hall stage is an electric angle 60°. However, there may be cases in which, due to the dispersion of magnetization of the sensor magnet in the brushless motor, the dispersion of the attachment position of the Hall sensor, or the like, as shown in FIG. 4B, the time period between two Hall edges that form each of the six Hall stages 1 to 6, that is, the time period of the Hall stage is not an electric angle 60°.
FIG. 4B shows a case in which the time periods of the Hall stages 1, 4 are less than an electric angle 60°. That is, the time period of the Hall stage 1 between the Hall edge which is a rising time point of the position detection signal Hu and the Hall edge which is a falling time point of the position detection signal Hw is an electric angle t1r which is less than an electric angle 60°. The time period of the Hall stage 4 between the Hall edge which is a falling time point of the position detection signal Hu and the Hall edge which is a rising time point of the position detection signal Hw is an electric angle t4r which is less than an electric angle 60°.
In such a case, during the period of the electric angle t1r, the motor control apparatus outputs a PWM signal (drive signal), for example, that repeats H and L to the inverter circuit in accordance with a power distribution pattern that corresponds to the Hall pattern 5 which represents the combination of electric potentials of the position detection signals Hu, Hv, Hw. During the period of the electric angle t4r, the motor control apparatus outputs a PWM signal that repeats H and L to the inverter circuit in accordance with a power distribution pattern that corresponds to the Hall pattern 2 which represents the combination of electric potentials of the position detection signals Hu, Hv, Hw.
That is, the motor control apparatus uses switching positions of three Hall sensors as criteria and rotates the brushless motor by outputting a drive signal to the inverter circuit that drives the brushless motor. However, actually, due to the dispersion of magnetization of the sensor magnet in the brushless motor, the dispersion of the attachment position of the Hall sensor, or the like, as shown in FIG. 4B, in the motor control apparatus, an actual rotor position and the Hall edge may be displaced from the electric angle 60°. In such a case, when switching the output of the drive signal for each Hall edge, there is a possibility that the switching may affect the motion of the brushless motor, and oscillation or an abnormal sound may occur.
Therefore, a motor drive apparatus is required having a configuration in which the position detection signal is corrected for each Hall edge that indicates switching of a Hall stage, and a power distribution pattern is switched on the basis of the corrected position detection signal.
Motor control apparatuses that prevents oscillation and an abnormal sound from occurring are described in Patent Documents 1, 2. However, the motor drive apparatuses described in Patent Documents 1, 2 does not have a configuration in which the position detection signal is corrected for each Hall edge that indicates switching of a Hall stage, and a power distribution pattern is switched on the basis of the corrected position detection signal. Therefore, it is not possible to prevent oscillation or an abnormal sound from occurring with good accuracy.